The invention relates to ink jet printers, to an improved nozzle plate for an ink jet printer and method for making the nozzle plate.
Ink jet printers continue to be improved as the technology for making the printheads continues to advance. New techniques are constantly being developed to provide low cost, highly reliable printers which approach the speed and quality of laser printers. An added benefit of ink jet printers is that color images can be produced at a fraction of the cost of laser printers with as good or better print quality than laser printers. All of the foregoing benefits exhibited by ink jet printers have also increased the competitiveness of suppliers to provide comparable printers in a more cost efficient manner than their competitors.
One area of improvement in the printers is in the print engine or printhead itself. This seemingly simple device is a relatively complicated structure containing electrical circuits, ink passageways and a variety of tiny parts assembled with precision to provide a powerful, yet versatile ink jet pen. The components of the pen must cooperate with each other and with a variety of ink formulations to provide the desired print properties. Accordingly, it is important to match the printhead components to the ink and the duty cycle demanded by the printer. Slight variations in production quality can have a tremendous influence on the product yield and resulting printer performance.
The primary components of the ink jet printhead are a semiconductor chip, a nozzle plate and a flexible circuit attached to the chip. The semiconductor chip is preferably made of silicon and contains various passivation layers, conductive metal layers, resistive layers, insulative layers and protective layers deposited on a device side thereof. For thermal ink jet printers, individual heater resistors are defined in the resistive layers and each heater resistor corresponds to a nozzle hole in the nozzle plate for heating and ejecting ink toward a print media.
The nozzle plates typically contain hundreds of microscopic nozzle holes for ejecting ink toward a print media. Separate nozzle plates are usually fabricated using laser ablation or other micro-machining techniques and are attached to the chips on a multi-chip wafer so that the nozzle holes align with the heater resistors. Each nozzle plate is individually attached to a corresponding chip on the wafer using an adhesive and the adhesive is cured.
Ink chambers and ink feed channels for directing ink to each of the ejection devices on the semiconductor chip are either formed in the nozzle plate material or in a separate thick film layer. In a center feed design for a top-shooter type printhead, ink is supplied to the ink channels and ink chambers from a slot or ink via which is conventionally formed by chemically etching or grit blasting through the thickness of the semiconductor chip. The chip, nozzle plate and flexible circuit assembly is typically bonded to a thermoplastic body using a heat curable and/or radiation curable adhesive to provide an ink jet pen.
The equipment used to form the nozzle plates and attach the nozzle plates to the chips is expensive and requires that close manufacturing tolerances be used. In order to decrease the cost of the printheads, newer manufacturing techniques using less expensive equipment is desirable. These techniques, however, must be able to produce printheads suitable for the increased quality and speed demanded by consumers. Thus, there continues to be a need for manufacturing processes and techniques which provide improved printhead components.
The invention provides a printhead for an ink jet printer and a method for making a printhead for an ink jet printer. The printhead includes a semiconductor substrate containing ink ejection devices and a dry-etched ink via therein for flow of ink from an ink supply to the ink ejection devices. A first photo-imaged polymer layer is applied to the semiconductor substrate, the first photo-imaged polymer layer being patterned and developed to contain ink flow chambers and ink flow channels corresponding to the ink ejection devices on the semiconductor substrate. A second photo-imaged polymer layer is applied to the first photo-imaged polymer layer. The second photo-imaged polymer layer is patterned and developed to contain nozzle holes corresponding to the ink chambers in the first photo-imaged polymer layer and corresponding to the ink ejection devices on the semiconductor substrate.
In another aspect the invention provides a method for making a printhead for an ink jet printer. The method includes providing a plurality of semiconductor devices on a silicon wafer, the wafer having a first surface and a second surface, the first surface containing ink ejection devices thereon. A first photo-imageable polymer layer is applied to the first surface of the silicon wafer and the first polymer layer is exposed to sufficient light radiation energy to provide a latent image of ink chambers and ink flow channels therein corresponding to the ink ejection devices. A second photo-imageable polymer layer is applied to the first photo-imageable polymer layer and the second polymer layer is exposed to sufficient light radiation energy to provide a latent image of nozzle holes therein corresponding to the ink ejection devices. A masking layer is applied to the second surface of the silicon wafer. The masking layer is exposed and developed to provide ink via patterns to be etched in the silicon wafer. The ink via patterns are dry etched through the silicon wafer up to the first polymer layer to form at least one ink via per semiconductor substrate. The latent images in the first and second polymer layers are developed to provide ink flow features and nozzles in the first and second polymer layers. The wafer containing the developed polymer layers is diced to provide a plurality of nozzle plate/substrate assemblies. At least one nozzle plate/substrate assembly containing the first and second developed polymer layers is attached to an electrical circuit and a printhead body to form an ink jet printhead.
In yet another aspect the invention provides a method for making a printhead for an ink jet printer. The method includes providing a semiconductor wafer containing a plurality of printhead chips, the wafer having a device surface and a second surface opposite the device surface. A first negative photoimageable material is applied to the device surface of the wafer. The first negative photoimageable material is dried to provide a first polymer layer. The first polymer layer is exposed to light radiation energy through a mask to provide exposed and unexposed areas of the first polymer layer. The unexposed areas are removed from the first polymer layer to provide ink channels and ink chambers in the first polymer layer. A positive photoresist material is applied to the first polymer layer to fill the ink channels and ink chambers in the first polymer layer. The positive photoresist material is exposed to light radiation energy to provide unexposed areas filling the ink chambers and ink channels and to provide exposed areas of the positive photoresist material. The exposed areas of the positive photoresist layer are removed from the first polymer layer. A second negative photoimageable material is applied to the first polymer layer and to the unexposed positive photoresist material. The second photoimageable material is dried to provide a second polymer layer. The second polymer is exposed to light radiation energy through a mask to provide unexposed areas corresponding to nozzle hole locations in the second polymer layer. The unexposed areas are removed from the second polymer layer to provide nozzle holes in the second polymer layer. A masking layer is applied to the second surface of the silicon wafer. The masking layer is exposed and developed to provide ink via patterns to be etched in the silicon wafer. The ink via patterns are dry etched through the silicon wafer up to the first polymer layer to form at least one ink via per semiconductor substrate. The positive photoresist material filling the ink channels and ink chambers is then removed from the wafer. The wafer is diced to provide a plurality of nozzle plate/chip assemblies. Flexible circuits or tape automated bonding (TAB) circuits are connected to the nozzle plate/chip assemblies to provide a plurality of printhead assemblies. At least one of the printhead assemblies is attached to a printhead body to provide an ink jet printhead.
An advantage of the invention is that it provides an improved printhead structure and method for making the printhead structure so as to avoid forming then attaching individual nozzle plates to a semiconductor substrate. Because the nozzle plate attaching step is avoided, alignment of the flow features in the nozzle plate with the ink ejection devices on the semiconductor substrate is greatly improved. Furthermore, because dry-etching is used to form the ink vias in the wafer, the ink vias may be formed after the first and second polymer layers are applied to the wafer. The invention also enables production of printhead devices having variable nozzle plate thicknesses without substantially affecting the planarity of the nozzle plate chip assembly.